Quantitative Assays for Catalytic Photo-Oxygenation of Alzheimer Disease-Related Tau Proteins

Abstract

Catalytic photo-oxygenation of tau amyloid is a potential therapeutic approach to tauopathies, including Alzheimer disease (AD). However, tau is a complex target containing great molecular size and heterogeneous isoforms/proteoforms. Although catalytic photo-oxygenation has been confirmed when using catalyst 1 and recombinant tau pretreated with heparin, its effects on tau from human patients have not yet been clarified. In this study, focusing on the histidine residues being oxygenated, we have constructed two assay systems capable of quantitatively evaluating the catalytic activity when used on human patient tau: (1) fluorescence labeling at oxygenated histidine sites and (2) LC–MS/MS analysis of histidine-containing fragments. Using these assays, we identified 2 as a promising catalyst for oxygenation of human tau. In addition, our results suggest that aggregated tau induced by heparin is different from actual AD patient tau in developing effective photo-oxygenation catalysts.

Leuco Ethyl Violet as Self‐Activating Prodrug Photocatalyst for In Vivo Amyloid‐Selective Oxygenation

“…Furthermore, we analyzed the effect of these catalysts on tau in the same samples, as aggregated tau is also photooxygenated by another catalyst. [ 60 ] The reaction with an AD patient‐derived tau is challenging due to its large molecular size and the presence of many isoforms and post‐translational modifications. We found that crosslink products of tau also increased following catalytic photooxygenation, especially when using 2 (Figure 6D ).…”

Small molecule amyloid disrupters demonstrate therapeutic efficacy for transthyretin amyloidosis

“…Building upon and expanding the horizons of catalysis medicine (13), our campaign to overcoming the irreversibility of amyloidosis has been founded upon the implementation of irreversible chemical modifications to amyloidogenic proteins for sufficient alteration of their chemical and physical properties. Using aerobic oxygen and visible light, in the presence of a photooxygenation catalyst harnessing a turn-on switch, activated upon binding to the cross-sheet quaternary structure characteristic to amyloids, preceding studies by our group have demonstrated covalent installation of hydrophilic oxygen atoms selectively to a series of amyloids including those associated with Alzheimer's disease (AD) (amyloid-β: Aβ and tau) (14)(15)(16), and Parkinson's disease (α-synuclein) (17,18) (Fig. 1B).…”

“…Consequently, we were obliged to revisit the foundational stages of our research, turning our focus to the screening of an array of photosensitizing catalysts in vitro. Structurally distinct small molecules from methylene blue (MB), a commercially available dye and a known disintegrator of Aβ under light irradiation (23), to original photooxygenation catalysts developed by our group (16,(20)(21)(22), were evaluated (Fig. 2A).…”

Histidine Photooxygenation Chemistry: Mechanistic Evidence and Elucidation

“…While the groundbreaking achievement showcased the effectiveness of a minimally‐invasive peripheral administration method, made possible by the blood‐brain barrier (BBB)‐permeable feature of 15 , accurately quantifying an intricate array of oxygenated histidine products under more clinically‐relevant environments, presented us with yet another obstacle to overcome. One of our most recent projects has provided a powerful platform to address this challenge, in which quantitative evaluation of photooxygenation on aggregated tau (another major protein that pathologically characterizes AD), from AD patients was demonstrated [33] . Our future efforts will be directed at addressing this in pursuit of developing novel therapeutic interventions that harness histidine photooxygenation.…”

“…One of our most recent projects has provided a powerful platform to address this challenge, in which quantitative evaluation of photooxygenation on aggregated tau (another major protein that pathologically characterizes AD), from AD patients was demonstrated. [33] Our future efforts will be directed at addressing this in pursuit of developing novel therapeutic interventions that harness histidine photooxygenation.…”